In general, a wafer is manufactured through a plurality of subdivided processes, and defects may be generated inside the wafer or on its surface during each process. Such defects may be classified into inherent defects such as cracks in a material itself, and external defects such as foreign substances attached to the wafer surface or contained therein. Defects generated during a process of manufacturing the wafer, depending on their positions and sizes, may result in the wafer having to be discarded. In particular, an air-pocket, a type of molding defect existing in an ingot, may be transferred to a bare wafer manufactured by slicing the ingot. In most cases, a wafer manufactured using a bare wafer having an air-pocket has to be discarded. Therefore, defects should be effectively detected at an appropriate time during the wafer manufacturing process.
One method of inspecting a wafer for defects is a reflective illumination method whereby light is radiated onto a wafer, reflected by the wafer, and detected using a line scan camera or an area camera. However, since this inspection method uses reflected light, a light source that emits with high linearity and intensity should be employed, and the illumination of a work space where the inspection apparatus is installed may have an effect on defect detection results. In addition, since the light source and the camera are disposed on the same space, the inspection apparatus may be quite large.
Another method of inspecting a wafer for defects is a transmissive illumination method whereby infrared radiation is modified according to characteristics of a wafer through which it is transmitted and detected using an infrared camera. An inspection apparatus using a transmissive illumination method is disclosed in U.S. Pat. No. 5,981,949.
FIG. 1 is a view of a conventional wafer defect inspection apparatus using a transmissive illumination method.
Referring to FIG. 1, the conventional wafer inspection apparatus includes a light source 10, a diffusion plate 14, an optical filter 13, a wafer fixing part 20, an infrared camera 22, a controller 28, a frame grabber 30, a computer 32, and a monitor 26.
The light source 10 is disposed opposite to one surface of the wafer 18 mounted on the wafer fixing part 20 to radiate light onto the wafer 18. The diffusion plate 14 is disposed between the light source 10 and the wafer 18 to uniformly distribute infrared light radiated from the light source 10. The optical filter 13 outputs only infrared wavelengths of the light output from the diffusion plate 14 to the wafer 18, or outputs only infrared wavelengths of the light output from the wafer 18 to the infrared camera 22. The infrared camera 22 is disposed opposite to the other side of the wafer 18 to detect the infrared light transmitted through the wafer 18 and output an image thereof. The controller 28 controls operation of the infrared camera 22, and selectively outputs an image input from the infrared camera 22 to the monitor 26 or the frame grabber 30. The frame grabber 30 digitizes the image input from the controller 28 and outputs the digitized image. The computer 32 analyzes the digitized image input from the frame grabber 30 to determine optical characteristics, defect density, and uniformity of the wafer.
The conventional wafer inspection apparatus having the above constitution can be manufactured to have a simple structure and a compact size, and a single wafer can be inspected within two minutes. However, the time consumed in inspecting a single wafer is much longer than when using an indirect illumination method, thus making it difficult to apply in an actual manufacturing process. In addition, since a plane array infrared camera capable of obtaining an image through a single photographing process and a diffusion plate having an optical transmissivity of 20%-60% are used, in order to obtain an image sufficient to detect defects in a wafer, a high-energy infrared light source should be used.